CONVICT LABOR FOR ROAD WORK. 81 



The following table gives commercial sizes of pneumatic tanks : ^ 

 Table 11. — Commercial sizes of pneumatic tanks. 



Diam- 

 eter. 



Length. 



Weight. 



Volume. 



Diam- 

 eter. 



Length. 



Weight. 



Volume. 



Inches. 



Feet. 



Pounds. 



Gallons. 



Inches. 



Feet. 



Pounds. 



Gallons. 



24 



6 



445 



140 



42 



10 



1,650 



720 



24 



8 



560 



195 



42 



12 



1,900 



865 



24 



10 



675 



245 



42 



14 



2,200 



1,000 



30 



6 



560 



220 



42 



16 



2,400 



1,150 



30 



8 



700 



295 



48 



10 



2,066 



1,000 



30 



10 



870 



365 



48 



12 



2,320 



1,130 



30 



12 



900 



440 



48 



14 



2,610 



1,300 



36 



6 



750 



315 



48 



16 



2,900 



1,500 



36 



■■ 8 



900 



420 



48 



■ 18 



3,600 



1,700 



36 



10 



1,050 



525 



48 



20 



3,950 



1,880 



36 



12 



1,200 



630 



48 



24 



4,650 



2,260 



42 



8 



1,450 



575 



60 



20 



5,900 



2,940 



As stated above, the water capacity of the tanks given in Table 11 

 will be not greater than three-fourths of the volume of the tank. 

 Therefore, for the camp of 40 convicts, assumed above, for which a 

 daily supply of 1,800 gallons is necessary, it is evident that a tank 48 

 inches in diameter and 14 feet long would be required and it would be 

 necessary to pump up this tank twice a day, starting with an initial 

 air pressure of at least 11 pounds. 



Pneumatic tanks usually are constructed to withstand safely a 

 pressure of 100 pounds per square inch. 



THE PNEUMATIC-PUMP METHOD. 



By the pneumatic-pump method the water is dtelivered direct from 

 the source. As it is not stored in a tank, storage capacity of other 

 form must be provided, either a special reservoir or a sufficiently 

 large dug well. The necessary apparatus consists of a small gasoline 

 engine, an air compressor, an air-tight steel pressure tank, and a pneu- 

 matic pump. The operation of the method is as follows: The gaso- 

 line engine supplies power to run the air compressor which pxmaps the 

 air in the tank up to any desired pressure. From this reservoir air 

 under pressure is supplied to the pneumatic pump which is immersed 

 in the water at its source in the well, lake, or brook. The pump con- 

 sists of two small metallic chambers; when a faucet is opened these 

 fill with water automatically and discharge alternately, owing to the 

 alternate application of the air pressure from the tank to the surface 

 of the water in each, and a continuous supply of fresh water is thus 

 forced through the pipes. 



Plate III shows a front and side view of a pneumatic pump and 

 the arrangement of a pnemnatic-pimip system. 



Each pump requires an air-pressure reducer, shut-off and release 

 cocks, and pressure gauge. TIk; air-pressure reducer is necessary to 

 reduce the high pressure carried in the tank to the uniform low pres- 



» Bulletin No. 57, U. 8. Department of Agriculture. 



